Polyvalent metal pectinate films and process of producing same



Patented Feb. 20, 1951 POLYVALENT METAL PECTINATE FILMS AND PROCESS OF PRODUCING SAME Harry S. Owens, Berkeley, and Thomas H. Schultz, Lafayette, Calif., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application June 10, 1947, Serial No. 753,793

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 16 Claims.

This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to us of any royalt thereon.

This invention relates to films, and in particular to films which are essentially composed of a polyvalent metal salt of a pectinic acid having a methoxyl content not greater t an 7.4%. The pectinic acid utilized is of high molecular weight with consequent high viscosity of water solutions or dispersions thereof. It may be produced by partial demethoxylation of pectin (pectin being the usual preparation of commerce extracted from various plant products, such as citrus peel or apple pomace without substantial demethoxylation) according to known procedures (see Patent No. 2,358,430, for example).

The pectinic acid herein referred to should be distinguished from pectic acid, the latter term pertaining to the acid produced by substantially complete demethoxylation of pectin. Pectinic acid has a methoxyl content between that of pectin and pectic acid, pectin having a methoxyl content of about to 14 percent depending largely on the source thereof. The methoxyl content of the pectinic acid may vary over a considerable range depending on the process of demethoxylation employed.

Superior films, from the standpoint of forming water-resistant films, are made from pectinic acids having a methoxyl content of below 6 percent. Films having greater elasticity can be made from pectinic acids having a higher methoxyl content. In general, according to the invention, the film is formed essentially from a polyvalent metal salt of a pectinic acid having a methoxyl content not greater than 7.4%. The salt above referred to means a salt of a pectinic acid with a polyvalent metal and is intended to include acid salts, i. e., those in which the carboXyl groups are not completely salifi'ed with the polyvalent metal.

According to one process of preparing the films, an aqueous solution of pectinic acid is first neutralized or partially neutralized with an inorganic hydroxide, such as an alkali metal or ammonium hydroxide, thus to form an alkali metal salt of the acid, an alkali metal hydrogen salt of the acid, an ammonium salt or an ammonium hydrogen salt of the acid. This material is then formed into an initial film and this film is immersed in an aqueous solution of a polyvalent metal salt.

The initial film can be formed in any desired manner, for instance, by extrusion into an alcohol solution, dipping, or simply by allowing a solution of the pectinate material to dry on a fiat surface. Any suitable polyvalent metal salt can be used for making the solution in which to dip the initial film, for instance, calcium chloride, chromium chloride, aluminum chloride, aluminum sulphate, zinc chloride, zinc sulphate, zinc nitrate, barium chloride, magnesium sulphate, magnesium chloride, strontium chloride, and suitable salts of titanium, molybdenum, iron, nickel, cobalt, copper, mercury, cadmium, lead and tin. It is only necessary that the solution contain the cations corresponding to the desired metal. Mixtures of salts, such as a mixture of calcium chloride and zinc chloride, can be used to obtain a film containing mixed metals, such as zinc and calcium. Concentration of the salt is not critical, and generally solutions of one normal concentration give good results. The metathesis takes place quite rapidly; generally 1 to 30 minutes yields complete reaction.

Examples I to XI exhibit the invention in detail according to the process more generally set forth above. In these examples, the intrinsic viscosity data were obtained in the usual manner expressing the concentration as grams of pectinic acid per ml. of solution. The measured solutions contained 0.9 percent sodium chloride in order to suppress the electro-viscous effect. The intrinsic viscosity was given by the expression:

Limit Q c 0 c where c is concentration sp is specific viscosity EXAMPLE I A sample of pectinic acid having an intrinsic viscosity of 5.2 and a methoxyl content of 4.5 percent was stirred with sufficient water to give a 1 percent solution, and sufiicient 0.5 N sodium hydroxide was added slowly with rapid stirring to raise the pH of the solution to 4.0. The solution was stirred for at least 30 minutes then centrifuged to remove suspended matter. Since the pectinic acid was approximately half-neutralized at the pH 4.0 indicated, the resulting material was a solution of sodium hydrogen salt of the pectinic acid.

Portions of the clarified solution were pipetted into shallow trays and evaporated. The resulting transparent, colorless films were carefully stripped from the trays.

A strip of the thus prepared sodium hydrogen salt of the acid film was gently stirred in a 1.0

EXAMPLE m Calcium and zinc salts of pectinic acid films were prepared as set forth in Example I, but starting with a pectinic acid having an intrinsic fif g g i gg g gagi g; $332 13; fi gi 5 viscosity of 4.4 and a methoxyl content of 7.4 salt of the pectinic acid thus formed was thus f fl i f i g washed with distilled water and dried by in- 856 es 6 m 6 same serting between 2 pieces of filter paper covering Sgt fmtth m the p examples the results bemg with a piece of glass and a weight and allowing 1o glven m the followmg Table it to remain in this condition overnight. Table 2 In a number of other examples, the same general procedure was followed. In some of Test Ca salt Zn salt them, 30 parts of a plasticizer per 100 parts of pectinic acid were added to the solution of so- Eensile strentglgl atkbrenk, ni s s in 14,202 14,30 dium hydrogen salt of the pectinic acid before i 't g it was centrifuged. Glycerol is a desirable plasos$$ l t figgn fi tlgiih 115 t y 230 2 2 gggt g g tg g g gg i f fggg L323 8f tilts 322th l3 tit, -80 l6. 0 Washed. m Water contammg glycerol smce 20 Another process of preparing the films involves 1f washed in water alone the glycerol tends to h f 1 f be washed from the films. Glycol bori-borate ex.luslon mug a 1e 0 a pee mm was also used as a plasticizer. Preparation of partly or complepely neutra1.1Zed.W1th an althis plasticizer is disclosed in U. s Patent t metal ammmum hydroxlde mto a Solu 1 953 741 Also in the other examples the polyp t polyvalent mgtal salt In this process a n'letal c'ation was varied by using the the nitial aqueous solution may have a concenchloride of the desired metal in place of the tration of 1 to 5 percent and a pH of about 4 to 6.

Stronger films are obtained at higher concencalclum chloride. When chromlc chloride was t f a t th f t used the 1 N solution was heated to 55 to 60 1 Ions 0 Pi ma mu concim ion 0 a two hours and then allowed to stand being the ability to obtain a solution which is not oemight to convert the green form too viscous to flow through the die. Any of the previously mentioned soluble polyvalent metal [CrClz (H2O)4]+ salts can be used in the polyvalent metal salt to the violet form solution. Generally, aqueous solutions of these as salts are satisfactory. In some cases, however, [Cr(H2O) sl with the pectinlc acids of higher methoxyl con- Tests of the various films were made aeeord tent, better results are obtained by including in m t0 the procedure indicated, the various the solution a substantial portion of an organic umns in Table 1 indicating the results under Solvent such as the appropriate headings. Example 2H1 exhibits the invention more spe- The Tensile strength at break column is clficany employmg the above descnbed that of the dry films which were previously cedurestored in a desiccator containing 36 percent sul- EXAMPLE m fur c acid to provide a relative humidity of 65 A pectinic d having methoxyl tent of i 1 s irre wi h wa er 0 give a percen so u ion determined by soaking the film in distilled water which was th tr at ith sodium hydroxide fsilg w g i gh p t ying with water wT r li e 1t to give a pH of 5.0. This solution was extriided I1 6 65 mg mac e as hrough a nozzle having a rec angular aper ure three columns indicate results of washing tests, of 0.7 by 70 mm, mm a precipitation bath the data showin th loss in w i h w h h consisting of 1 N calcium chloride and 0.02 N PS d. fi in dist lled Wate a 2 C. hydrochloric acid. The extrusion rate was apfctlzrlzgoliro glgulsgsecondhirif Ofil percertfllzlagcoa proximately 2.6 ltnl. per second, and the film was a a an r in drawn through he bath at the rate of 5.6 cm.- 1 percent soap flakes at 40 to 50 C. for oneper second. The bath had an effective length of half hour; following the washing, the strips being 30 inches. The film was removed from the bath rinsed in distilled water and dried at percent on godet rolls and passed into a water bath surfirelative humidity before final weighing. ciently long to give complete washing. After- Table 1 sttlftt i Wei titt tiilt tfliilt Example Cation Plasticizer alt) break, ggg i' i g washted vlvqastlgn washed 5. r 1 i sq. per cent or dry pez e t pgr cent gt ar g t 4.0 21 o s 5 3.5 28 o s 9 3.0 29 0 in 2 o o 5.5 20 1 11 s 6.5 20 1 a 16 3.5 23 o 100 45 5.2 28 1 o 0 8.0 28 10 1s 20 4.7 31 lo 100 53 drying, at strong film of the calcium salt of pec-' tinic acid was obtained.

As before indicated, thefilms may contain Water-soluble plasticizers. The plasticizer -may be added to the solution from which the film is made. In the washing of films containing glycerol or other low molecular Weight, watersoluble substances, the wash water should contain the same plasticizer to prevent removal of the plasticizer from the film by the wash water.

The incorporation of a plasticizer is advantageous to increase the stretch and improve the folding endurance of the film. Water-soluble plasticizers have proved best for this purpose, for instance, tartaric acid, glycol, glycol mono-methyl ether, glycol monoethyl ether, and so forth, in addition to those previously mentioned. The proportion of plasticizer should not be more than about 30 percent (based on the amount of pectinic acid). Higher proportions than this value tend to cause considerable reduction in the tensile strength of the film.

The films of this invention are self-sustaining, odorless, non-fibrous, transparent, flexible, and strong. They can be used for wrapping articles to protect them from dust, dirt, oil, or other contamination. The films of zinc, aluminum, and calcium pectinates, especially the first two mentioned, are particularly desirable, in that they are flame-resistant. Especially good flameproofing films can be made by incorporating known flame-resisting agents, such as sodium boro-phosphate, for instance, into the zinc or aluminum salt of the pectinic acid film. The film of the calcium salt of the acid is non-allergenic and can be employed in surgical operations as a separatant to prevent adhesions. Copper, lead, zinc, and other salts of the acid form films which are toxic to micro-organisms and can be used to protect articles from such attack. Thus, a film of the zinc salt of pectinic acid can be employed to make cloth resistant both to flame and mildew.

Films produced according to the examples may be used as wrappings in the regular manner.

However, they may also be used as permanent coatings by attaching them to articles with adhesives. A dispersion of the metal salt of the pectinic acid may be used as an adhesive for this purpose.

When it is desired that the film be permanently attached to the article, it may also be formed directly thereon by dipping the article in a hot dispersion of the polyvalent metal salt. Aqueous dispersions containing 1 to 8 percent of the polyvalent metal salt and heated to about 50 to 90 C. give best results. Upon immersion of the article in such dispersion, removal therefrom and exposure to air, a gel-like coating is formed. Upon drying, a tough film results.

If desired, a film may be formed on an article having a non-coherent surface, by dipping in the manner indicated above, and after drying, the film may be peeled from the article, thus to produce a separate film.

In order to obtain a dispersion of an efiicient concentration, it is sometimes necessary in this type of procedure to limit the amount of polyvalent metal cation with respect to the carboxyl groups present in the pectinic acid. Generally, the proportion of polyvalent metal cation carboxyl groups ranges from completely salified to /8 salified. It has been found that if the peetinic acid has a low methoxyl content, it should be only partly salified. If on the other hand the pectinic acid has ahigh methoxyl content, the carboxyl groups may in some case be substantially completely salified. The criterion here is togeta. dispersion which is. not too viscous to fiow properly and one which will give a good'gel-like coating when. the article is immersed therein-. Wherethe pectinic acid'has been only partially salified, the film so formed can,v if desired, besubsequently immersed in a solution containing the desired cation-whereby alL'the carboxyl groups will become salified.

Having thus described.theinvention, what is claimed is::

1. A process of producing a film comprising pectinic acid having a methoxyl content not greater than 7.4% with an inorganic hydroxide at least partially to neutralize the pecintic acid, forming a film of the material thus obtained, and contacting the film with an aqueous solution of a water-soluble polyvalent metal salt.

2. The process of claim 1 characterized in that a water-soluble plasticizer in amount not to exceed 30 percent of the pectinic acid is mixed with the material before it is formed into the film.

3. The process of claim 1 characterized in that the film of the material is formed by plating the material onto a non-adherent surface and then peeling it from the surface, and thereafter contacting the film with the equeous soution of the water-soluble polyvalent metal salt.

4. The process of claim 1 characterized in that the film of the material is formed and contacted with the aqueous solution of the watersoluble polyvalent metal salt by extruding the film of the material into the solution.

5. The process of claim 1 characterized in that the metal salt is one which yields zinc cations in the aqueous solution.

6. The process of claim 1 characterized in that the metal salt is one which yields calcium cations in the aqueous solution.

7. The process of claim 1 characterized in that the metal salt is one which yields chromium cations in the aqueous solution.

8. A film composed essentially of a polyvalent metal salt of a pectinic acid having a methoxyl content not greater than 7.4

9. A film composed essentially of a polyvalent metal salt of a pectinc acid having a methoxyl cont nt not greater than 7.4% plasticized with a water-soluble plasticizer.

10. The film of claim 9 characterized in that the plasticizer is glycerol.

11. A film composed essentially of the zinc salt of a pectinic acid having a methoxyl content not, greater than 7.4%.

12. A film composed essentially of the calcium salt of a pectin c acid having a methoxyl content not greater than 7.4

13. A film composed essentially of the chromium salt of a pectinic acid having a methoxyl content not greater than 7.4%.

14. The film of claim 11 plasticized with glycol bori-borate.

15. The film of claim 12 plasticized with glycol bori-borate.

16. The film of claim 12 plasticized with glycerol.

HARRY S. OWENS. THOMAS H. SCHULTZ.

(References on following page) 7 8 REFERENCES CITED Number Name Date The following references are of record in the 2,163,521 Myers e 1939 file of this patent: 2,3 5,6 Hegan y 1945 UNITED STATES PA Ts 2,407,635 Engler Sept. 17, 1946 5 FOREIGN PATENTS Number Name Date Nurr ber Country Date 1,634,879 Nanji July 5, 1927 Bennett p 3 Great Brltflln June 1 1,973,613 Cowgill Sept. 11, 1934: OTHER REFERENCES 3,614 COWgill Sept. 1934 10 Uses and Application of Chemicals and Re- 2,027,682 Eichmaml a 14, 1936 lated Materials, Gregory, vol. II (1944), pages 2,032,687 Cowgill Mar. 3, 1936 155 and 156.

2,155,361 Myers Apr. 18, 1939 

1. A PROCESS OF PRODUCING A FILM COMPRISING PECTINIC ACID HAVING A METHOXYL CONTENT NOT GREATER THAN 7.4% WITH AN INORGANIC HYDROXIDE AT LEAST PARTIALLY TO NEUTRALIZE THE PECINTIC ACID, FORMING A FILM OF THE MATERIAL THUS OBTAINED, AND CONTACTING THE FILM WITH AN AQUEOUS SOLUTION OF A WATER-SOLUBLE POLYVALENT METAL SALT. 